Not many years ago, the idea of an encyclopedia of autoimmune diseases would have been inconceivable. The reason is not that there were no autoimmune diseases; in fact, they have been with us from time immemorial. It is rather because we were not in the habit of thinking of the autoimmune diseases as a group. The explanation is quite understandable. The autoimmune diseases, which result from the pathological effects of a misguided, self-directed immune response, can affect essentially any site in the body.
There is an autoimmune disease of the skin, brain, heart, liver, lung, kidney, joints, and so forth. The clinical presentation of the disease depends upon its location, and, therefore, it varies greatly from one disease to another. Equally important, the treatment of the different autoimmune diseases falls to different medical specialists, who are usually arranged according to the organ system with which they are concerned. Thus, particular autoimmune diseases are cared for by physicians specializing in dermatology, neurology, cardiology, gastroenterology, nephrology, rheumatology, etc.
There was, in the past, very little reason or incentive for bringing these disparate disorders together into a single category.
A transformation occurred toward the end of the 20th century when medical scientists began to find that there is a remarkable commonality among these diseases. First, the misguided immune response causes, or at least contributes significantly, to the progression of the disease. Our newer knowledge of the immune response, acquired from basic research, has allowed us to understand a great deal more about the factors that normally regulate the immune response and where they might go wrong. We now realize that autoimmunity (an immune response directed to oneself) is actually quite common. This concept violated some of the most basic early tenets of immunology and took some time to be accepted. Although most autoimmune responses are limited and harmless, sometimes an immune response to oneself goes too far and produces the type of injury we recognize as autoimmune disease.